The present invention relates to rotary vane pumps or sliding vane pumps. More particularly, the present invention relates to an improved cam arrangement having advantageously configured inlet and outlet openings, a mathematical non-symmetrical cam profile, a fluid energizing port arrangement, and an improved thrust absorber, and other improvements.
Sliding vane pumps are disclosed in U.S. Pat. No. 4,746,280 and 4,830,593. In a sliding vane pump the pump casing can include a stationary liner having an inner surface eccentric with respect to an axis of a rotor held within. A plurality of radial slots are arranged in the rotor which hold, in each slot, a vane slidably extendable and retractable therein. Around the periphery of the liner are arranged, in select regions, inlet openings and outlet openings. The fluid enters the inlet openings and is trapped between the rotor and the liner between adjacent moving vanes. The fluid is then moved around the interior of the liner with the rotating rotor until the fluid is passed through the outlet openings. The vanes or blades must be strategically biased radially outward either by springs or, in some cases, hydraulic pressure of the fluid being pumped.
Vane pumps are particularly useful in pumping fluids which are close to their boiling temperature at pressure, i.e., where very low suction head is available. In these applications, cavitation is a problem with its corresponding vibration and noise. Cavitation is commonly encountered during the liquid transfer of high vapor pressure products (boiling liquids) such as liquified petroleum gasses and ammonia. Such products, when transferred from one container to another, will boil (liquid/vapor transformation) in the pump inlet and pump chamber when the internal suction pressure is no longer at equilibrium. The liquid to vapor formation change can be caused by (1) the physical transfer of product from one closed vessel to another, or (2) the absence of a vapor equalizing line which allows vapor pressure between tanks to equalize and reduce or eliminate the liquid/vapor transformation (boiling) during transfer.
A high vapor pressure product, as described above, when being transferred (pumped) via piping, easily experiences phase changes, from liquid to vapor and back to liquid, resulting in the pump having to operate with a liquid/vapor mix. This mixture can cause internal moving parts, such as vanes, to become unstable because of incomplete filling of the pumping chamber with liquid.
An additional problem with prior art pumps is that the drive for the pump, when used in a truck loading operation, comprises a power take off shaft from the transmission which is rotationally driven elevationally offset from the axis of the pump. A drive shaft with U joints or knuckle joints is needed to couple the take off shaft to the pump shaft. This has a tendency to transmit axial movement of the drive shaft to the pump shaft or a bending moment on the pump shaft because of the offset.